U.S. patent number 11,022,372 [Application Number 16/019,618] was granted by the patent office on 2021-06-01 for air conditioner.
This patent grant is currently assigned to HITACHI-JOHNSON CONTROLS AIR CONDITIONING, INC.. The grantee listed for this patent is Hitachi-Johnson Controls Air Conditioning, Inc.. Invention is credited to Takeshi Endo, Mamoru Houfuku, Kenji Matsumura, Nagatoshi Ooki, Shuuhei Tada.
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United States Patent |
11,022,372 |
Tada , et al. |
June 1, 2021 |
Air conditioner
Abstract
An air conditioner that includes a heat exchanger including:
heat-transfer pipes extending in a horizontal direction and spaced
apart at predetermined intervals in a vertical direction and
configured to allow a thermal medium to flow therein. A part of the
heat transfer pipes are used for at least one inflow path into
which the thermal medium flows from the outside of the heat
exchanger and the other part of the heat transfer pipes are used
for at least one outflow path from which the thermal medium flows
out to the outside. At least one connection pipe through which an
outlet side of one of the at least one inflow path communicates
with an inlet side of one of the at least one outflow path.
Inventors: |
Tada; Shuuhei (Tokyo,
JP), Matsumura; Kenji (Tokyo, JP), Ooki;
Nagatoshi (Tokyo, JP), Houfuku; Mamoru (Tokyo,
JP), Endo; Takeshi (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi-Johnson Controls Air Conditioning, Inc. |
Tokyo |
N/A |
JP |
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Assignee: |
HITACHI-JOHNSON CONTROLS AIR
CONDITIONING, INC. (Tokyo, JP)
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Family
ID: |
62840491 |
Appl.
No.: |
16/019,618 |
Filed: |
June 27, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20180306515 A1 |
Oct 25, 2018 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2017/043016 |
Nov 30, 2017 |
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Foreign Application Priority Data
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Jan 13, 2017 [JP] |
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JP2017-004542 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28D
1/0417 (20130101); F28D 1/0535 (20130101); F28F
1/422 (20130101); F28F 9/0253 (20130101); F28F
1/32 (20130101); F28F 9/0265 (20130101); F28F
1/022 (20130101); F28F 9/027 (20130101); F28D
1/05383 (20130101); F25B 39/00 (20130101); F28F
9/0243 (20130101); F28F 23/00 (20130101); F28D
1/024 (20130101); F28F 9/0209 (20130101); F28D
2021/0068 (20130101); F28F 1/04 (20130101); F28F
2250/06 (20130101); F24F 13/30 (20130101); F24F
11/89 (20180101) |
Current International
Class: |
F28D
1/053 (20060101); F28D 1/04 (20060101); F28F
1/32 (20060101); F25B 39/00 (20060101); F28F
9/02 (20060101); F28F 1/02 (20060101); F28F
1/42 (20060101); F28F 23/00 (20060101); F28D
1/02 (20060101); F24F 13/30 (20060101); F24F
11/89 (20180101); F28F 1/04 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2001-304621 |
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Oct 2001 |
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JP |
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2007-163013 |
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Jun 2007 |
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JP |
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2013-053812 |
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Mar 2013 |
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JP |
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2013-228154 |
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Nov 2013 |
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JP |
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2015-127619 |
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Jul 2015 |
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JP |
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2016-053473 |
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Apr 2016 |
|
JP |
|
2016053473 |
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Apr 2016 |
|
JP |
|
Other References
International Search Report and Written Opinion of
PCT/JP2017/043016 dated Feb. 20, 2018. cited by applicant.
|
Primary Examiner: Ruppert; Eric S
Attorney, Agent or Firm: Mattingly & Malur, PC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of
PCT/JP2017/043016, filed on Nov. 30, 2017, which claims priority to
Japanese Patent Application No. 2017-004542, filed on Jan. 13,
2017, the contents of which are hereby incorporated by reference in
their entireties.
Claims
The invention claimed is:
1. An air conditioner, comprising: a heat exchanger, which
comprises: a plurality of heat-transfer pipes arranged to extend in
a horizontal direction and to be spaced apart at predetermined
intervals in a vertical direction and configured to allow a thermal
medium to flow therein, wherein the heat transfer pipes comprise a
plurality of inflow paths into which the thermal medium flows from
an outside of the heat exchanger and the heat transfer pipes
comprise a plurality of outflow paths from which the thermal medium
flows out to the outside of the heat exchanger; and a plurality of
connection pipes including a first connection pipe and a second
connection pipe, wherein an outlet side of a first inflow path, of
the plurality of inflow paths, communicates with an inlet side of a
first outflow path, of the plurality of outflow paths, via the
first connection pipe, wherein the first outflow path is disposed
below the first inflow path, wherein an outlet side of a second
inflow path, of the plurality of inflow paths, communicates with an
inlet side of a second outflow path, of the plurality of outflow
paths, via a second connection pipe, wherein the second outflow
path is disposed above the second inflow path, and wherein at least
one connection pipes has a hydraulic diameter of 4 mm or
greater.
2. The air conditioner of claim 1, wherein at least one of the
plurality of connection pipes has a hydraulic diameter of 11 mm or
less.
3. The air conditioner of claim 1, wherein each of the plurality of
heat-transfer pipes is constituted by a tubular member with a cross
section having a substantially oval shape, the tubular member
having an interior divided into a plurality of flow channels
extending in a length direction of the tubular member.
4. The air conditioner of claim 1, wherein the thermal medium
comprises at least one of the group consisting of R410A, R404A,
R32, R1234yf, R1234ze(E), and HFO1123.
5. A heat exchanger, comprising: a plurality of heat-transfer pipes
arranged to extend in a horizontal direction and to be spaced apart
at predetermined intervals in a vertical direction and configured
to allow a thermal medium to flow therein, wherein the heat
transfer pipes comprise a plurality of inflow paths into which the
thermal medium flows from an outside of the heat exchanger and the
heat transfer pipes comprise a plurality of outflow paths from
which the thermal medium flows out to the outside of the heat
exchanger; and a plurality of connection pipes including a first
connection pipe and a second connection pipe, wherein an outlet
side of a first inflow path, of the plurality of inflow paths,
communicates with an inlet side of a first outflow path, of the
plurality of outflow paths, via the first connection pipe, wherein
the first outflow path is disposed below the first inflow path,
wherein an outlet side of a second inflow path, of the plurality of
inflow paths, communicates with an inlet side of a second outflow
path, of the plurality of outflow paths, via a second connection
pipe, wherein the second outflow path is disposed above the second
inflow path, and wherein at least one of the plurality of
connection pipes has a hydraulic diameter of 4 mm or greater.
6. The heat exchanger of claim 5, wherein the at least one of the
plurality of connection pipes has a hydraulic diameter of 11 mm or
less.
7. The heat exchanger of claim 5, wherein each of the plurality of
heat-transfer pipes is constituted by a tubular member with a cross
section having a substantially oval shape, the tubular member
having an interior divided into a plurality of flow channels
extending in a length direction of the tubular member.
8. The heat exchanger of claim 5, wherein the thermal medium
comprises at least one of the group consisting of R410A, R404A,
R32, R1234yf, R1234ze(E), and HFO1123.
Description
BACKGROUND
1. Field of the Invention
The present invention relates to an air conditioner having a heat
exchanger.
2. Description of Related Art
Various proposals have been made for improving heat-exchange
efficiency of heat exchangers of air conditioners.
For example, Japanese Patent Application Publication No. 2013-53812
presents proposals related to a heat exchanger in which a plurality
of heat-transfer pipes extending in a horizontal direction are
disposed at predetermined intervals in a vertical direction and
header pipes extending in the vertical direction are provided at
opposite ends of the plurality of heat transfer pipes. The interior
of each header pipe is divided into a plurality of sections by
partition plates. Refrigerant circulating in the heat exchanger
flows downward while flowing through the heat-transfer pipes in
both directions between the header tubes. Corrugated fins are
interposed between the heat-transfer pipes. The refrigerant
transfers heat to/from (exchanges heat with) an air flow passing
the corrugated fins while the refrigerant passes through the
heat-transfer pipes.
When the heat exchanger described above is used as a condenser,
refrigerant in a gaseous state (gas refrigerant) gives off heat to
an air flow (i.e., the refrigerant is cooled by the air flow) to
condense into refrigerant in a liquid state (liquid
refrigerant).
As the volume of the liquid refrigerant does not further diminish
even when it is cooled, a liquid pool of the liquid refrigerant is
formed in the heat-transfer pipes to narrow the region in which the
gas refrigerant can give off heat to condense, resulting in a
decrease in the heat-exchange efficiency. In view of the above, it
is desirable to inhibit formation of the liquid pool of the liquid
refrigerant.
As to the amount of refrigerant to be sealed, an insufficient
amount of refrigerant cannot demonstrate desired heat exchange
performance, whereas an excessive amount of refrigerant increases
production costs.
Moreover, taking into account the Global Warming Potential (GWP) of
the refrigerant to be used, it is desirable to avoid unnecessarily
increasing the amount of refrigerant to be sealed.
The present invention has been made in view of the above
circumstances and it is an object of the present invention to
provide an air conditioner that can inhibit formation of a liquid
pool in a heat exchanger to improve the heat-exchange efficiency
and allow sealing an appropriate amount of refrigerant into the
heat exchanger.
SUMMARY
To achieve the above-described object, an air conditioner according
to the present invention includes a heat exchanger that includes: a
plurality of heat-transfer pipes arranged to extend in a horizontal
direction and to be spaced apart at predetermined intervals in a
vertical direction and configured to allow a thermal medium to flow
therein, wherein a part of the plurality of heat transfer pipes are
used for at least one inflow path into which the thermal medium
flows from an outside of the heat exchanger and the other part of
the plurality of heat transfer pipes are used for at least one
outflow path from which the thermal medium flows out to the outside
of the heat exchanger; and at least one connection pipe through
which an outlet side of one of the at least one inflow path
communicates with an inlet side of one of the at least one outflow
path, the at least one connection pipe having a hydraulic diameter
of 4 mm or greater. A circulation flow rate Gr kg/s of the thermal
medium and the number of the paths N satisfy
0.003.ltoreq.Gr/N.ltoreq.0.035.
Advantageous Effects of the Invention
The present invention provides an air conditioner that can inhibit
formation of a liquid pool in a heat exchanger to allow for sealing
an appropriate amount of refrigerant into the heat exchanger while
improving the heat-exchange efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram representing the refrigeration cycle system of
an air conditioner according to a present embodiment.
FIG. 2 is a perspective view showing a heat exchanger of the air
conditioner according to the present embodiment.
FIG. 3 is an exploded perspective view illustrating the heat
exchanger disassembled into a heat exchange section and
headers.
FIG. 4 is a perspective view of a heat-transfer pipe of the heat
exchanger.
FIG. 5 is a schematic view illustrating the configuration of the
heat exchanger according to the present embodiment.
FIG. 6 is a cross-sectional view of a connection portion of the
heat exchanger according to the present embodiment, which
connection portion connects a fold back header of the heat
exchanger to the heat exchange section of the heat exchanger.
FIG. 7 is a graph illustrating the relationship between the
circulation flow rate of refrigerant per path and the pressure
loss.
FIG. 8 is a graph illustrating the relationship between the
circulation flow rate of refrigerant per path and the Froude
number.
FIG. 9 is a graph illustrating the relationship between the
hydraulic diameter and the pressure loss of a connection pipe.
FIG. 10 is a diagram illustrating the relationship between the
hydraulic diameter of a connection pipe and the amount of
refrigerant holding capacity per path.
FIG. 11 is a cross-sectional view of another configuration for the
connection portion connecting the fold back header and the heat
exchange section of the heat exchanger according to the present
embodiment.
EMBODIMENTS FOR CARRYING OUT THE INVENTION
Embodiments for carrying out the present invention will now be
described in detail with reference to the drawings. In the
description, the same symbols will be assigned to the respective
same elements, and duplicative description will be omitted.
<Configuration of Air Conditioner>
FIG. 1 illustrates the refrigeration cycle of an air conditioner 1
in which the heat exchanger 101 according to the present invention
is employed.
The air conditioner 1 has an outdoor unit 10 and an indoor unit
30.
The outdoor unit 10 has a compressor 11, a four-way valve 12, an
outdoor heat exchanger 13, an outdoor blower 14, an outdoor
expansion valve 15, and an accumulator 20.
The indoor unit 30 has an indoor heat exchanger 31, an indoor
blower 32, and an indoor expansion valve 33.
The devices of the outdoor unit 10 and the devices of the indoor
unit 30 are connected by a refrigerant piping 2 to form a
refrigeration cycle. Refrigerant serving as a thermal medium is
sealed in the refrigerant piping 2. The refrigerant circulates
between the outdoor unit 10 and the indoor unit 30 via the
refrigerant piping 2.
Next, a description will be given of the devices of the outdoor
unit 10.
The compressor 11 sucks and compresses refrigerant in a gaseous
state (gas refrigerant) and discharges the compressed
refrigerant.
The four-way valve 12 changes the direction of refrigerant flowing
between the outdoor unit 10 and the indoor unit 30 while
maintaining the direction of refrigerant flowing toward the
compressor 11. The four-way valve 12 switches between cooling and
heating operations by changing the direction of the
refrigerant.
The outdoor heat exchanger 13 has a heat exchanger 101 according to
the present invention to exchange heat between the refrigerant and
outdoor air.
The outdoor blower 14 supplies the outdoor air to the outdoor heat
exchanger 13.
The outdoor expansion valve 15 is a throttle valve for causing
refrigerant in a liquid state (liquid refrigerant) to evaporate by
adiabatic expansion.
The accumulator 20 is provided to accumulate liquid return in a
transitional state. The accumulator 20 separates liquid refrigerant
mixed in gas refrigerant to be supplied to the compressor 11 to
maintain a moderate quality of the refrigerant.
Next, a description will be given of the devices of the indoor unit
30.
The indoor heat exchanger 31 has a heat exchanger 101 according to
the present invention to exchange heat between refrigerant and
indoor air.
The indoor blower 32 supplies the indoor air to the indoor heat
exchanger 31.
The indoor expansion valve 33 is a throttle valve for causing
refrigerant in a liquid state (liquid refrigerant) to evaporate by
adiabatic expansion. The indoor expansion valve 33 is capable of
changing the aperture size thereof to change the flow rate of
refrigerant flowing in the indoor heat exchanger 31.
<Operation of Air Conditioner>
Next, a description will be given of a cooling operation of the air
conditioner 1 by which cool air is supplied into a room.
The solid arrows in FIG. 1 represent the flow of refrigerant in the
cooling operation. The four-way valve 12 controls the direction of
the flow as indicated by the solid lines.
The gas refrigerant compressed to high-temperature and
high-pressure by the compressor 11 flows into the outdoor heat
exchanger 13 via the four-way valve 12.
The gas refrigerant that has flowed into the outdoor heat exchanger
13 gives off heat to the outdoor air supplied by the outdoor blower
14, to condense into a low-temperature, high-pressure liquid
refrigerant.
That is, the outdoor heat exchanger 13 functions as a condenser in
the cooling operation.
The liquid refrigerant that has condensed from the gas refrigerant
is sent to the indoor unit 30 via the outdoor expansion valve 15.
As the outdoor expansion valve 15 does not function as an expansion
valve in this process, the liquid refrigerant passes through the
outdoor expansion valve 15 as is without adiabatic expansion.
The liquid refrigerant that has flowed into the indoor unit 30
adiabatically expands in the indoor expansion valve 33 and flows
into the indoor heat exchanger 31.
The liquid refrigerant takes latent heat of vaporization from the
indoor air supplied by the indoor blower 32, to evaporate into a
low-temperature, low-pressure gas refrigerant.
That is, the indoor heat exchanger 31 functions as an evaporator in
the cooling operation.
The indoor air is relatively cooled by being deprived of latent
heat of vaporization, resulting in cool air blowing into the
room.
The gas refrigerant that has evaporated from the liquid refrigerant
is sent to the outdoor unit 10.
The gas refrigerant that has returned to the outdoor unit 10 passes
through the four-way valve 12 and flows into the accumulator
20.
The liquid refrigerant mixed in the gas refrigerant having flowed
into the accumulator 20 is separated in the accumulator 20,
adjusted to have a predetermined quality, and supplied to the
compressor 11 to be compressed again.
In this way, the cooling operation for providing cool air indoors
is achieved by circulating the refrigerant in the directions
indicated by the solid arrows in the refrigeration cycle.
That is, in the cooling operation, the outdoor heat exchanger 13
functions as a condenser and the indoor heat exchanger 31 functions
as an evaporator.
Next, a description will be given of a heating operation of the air
conditioner 1 by which warm air is supplied into the room.
The dotted arrows in FIG. 1 represent the flow of refrigerant in a
heating operation. The four-way valve 12 controls the direction of
the flow as indicated by the dotted lines.
The gas refrigerant that has been compressed to high-temperature
and high-pressure by the compressor 11 flows into the indoor unit
30 via the four-way valve 12.
The gas refrigerant that has flowed into the indoor heat exchanger
31 gives off heat to the indoor air supplied by the indoor blower
32 while passing through the indoor heat exchanger 31, to condense
into a low-temperature, high-pressure liquid refrigerant.
That is, the indoor heat exchanger 31 functions as a condenser in
the heating operation.
The indoor air is relatively heated by receiving heat, resulting in
warm air blowing into the room.
The liquid refrigerant that has condensed from the gas refrigerant
passes the indoor expansion valve 33 to be sent to the outdoor unit
10. As the indoor expansion valve 33 does not function as an
expansion valve in this process, the liquid refrigerant passes
through the indoor expansion valve 33 as is without adiabatic
expansion.
The liquid refrigerant that has flowed into the outdoor unit 10
adiabatically expands in the outdoor expansion valve 15 and flows
into the outdoor heat exchanger 13.
The liquid refrigerant takes latent heat of vaporization from the
outdoor air supplied by the outdoor blower 14, to evaporate into a
low-temperature, low-pressure gas refrigerant.
That is, the outdoor heat exchanger 13 functions as an evaporator
in the heating operation.
The refrigerant that has flowed out of the outdoor heat exchanger
13 passes through the four-way valve 12 and flows into the
accumulator 20.
The liquid refrigerant mixed in the refrigerant having flowed into
the accumulator 20 is separated in the accumulator 20, adjusted to
have a predetermined quality, and supplied to the compressor 11 to
be compressed again.
In this way, a heating operation for providing warm air indoors is
achieved by circulating the refrigerant in the directions indicated
by the dotted arrows in the refrigeration cycle.
That is, in the heating operation, the indoor heat exchanger 31
functions as a condenser and the outdoor heat exchanger 13
functions as an evaporator.
Next, a description will be given of the heat exchanger 101
according to the present embodiment, which constitutes each of the
above-described outdoor heat exchanger 13 and the indoor heat
exchanger 31.
The outdoor heat exchanger 13 and the indoor heat exchanger 31 in
the above described air conditioner 1 are each constituted by the
heat exchanger 101 of the present invention. It should be noted
that the heat exchanger 101 exerts effects of the present invention
even when only one of the outdoor heat exchanger 13 and the indoor
heat exchanger 31 is constituted by the heat exchanger 101.
As shown in FIGS. 2 and 3, the heat exchanger 101 according to the
present embodiment is a fin-tube type heat exchanger and has a heat
exchange section 110 and headers 130.
The heat exchange section 110 is a part to exchange heat between
refrigerant and air. The heat exchange section 110 has a plurality
of heat-transfer fins 111 and a plurality of heat-transfer pipes
112 (see FIG. 3)
The plurality of heat-transfer fins 111 are each constituted by a
rectangular, plate-shaped member. The plurality of heat-transfer
fins 111 are arranged in a stacked manner such that the rectangular
plate-shaped members have their length directions in the vertical
direction and are spaced apart at predetermined intervals, with
adjacent rectangular plate-shaped members facing with each other.
The outdoor air or indoor air passes through gaps between the
stacked heat-transfer fins 111.
As shown in FIG. 4, each heat-transfer pipe 112 is constituted by a
flat tubular member with a cross section having a substantially
oval shape. The interior of the flat tubular member is divided by
partition walls 113 into a plurality of flow channels 114 extending
in the length direction of the flat tubular member. The
heat-transfer pipes 112 have upper and lower portions that
correspond to flat portions of the oval shape and extend in the
horizontal direction, and are spaced apart at predetermined
intervals in the vertical direction. The heat-transfer pipes 112
penetrate the stacked heat-transfer fins 111 and are joined
thereto.
The heat-transfer pipes 112 each have opposite ends that
communicate with respective headers 130.
In the use of the heat exchanger 101 as a condenser, the plurality
of heat-transfer pipes 112 provide inflow paths 121 into which the
refrigerant (gas refrigerant) flows from the outside and outflow
paths 122 from which the refrigerant (liquid refrigerant) flows out
to the outside.
As shown in FIG. 5, in the heat exchanger 101 according to the
present embodiment, the inflow paths 121 and the outflow paths 122
are alternately arranged in the vertical direction. The inflow
paths 121 and the outflow paths 122 are not necessarily alternately
arranged in the vertical direction if they are arranged such that
they are not likely to be influenced by the gravity.
In the condenser, the ratio of gas refrigerant to the whole
refrigerant is high upstream of the heat exchange section 110,
whereas the ratio of liquid refrigerant to the whole refrigerant
increases as the refrigerant flows downstream. That means that the
volume of the refrigerant in each outflow path 122 is smaller than
that in the corresponding inflow path 121. In FIG. 6, for
simplicity of drawing, each inflow path 121 and each outflow path
122 have the same number of heat-transfer pipes 112. However, it is
desirable to select the number of heat-transfer pipes for each path
so that refrigerant flows at a necessary speed in accordance with
whether the refrigerant flowing through the path is in a condensed
state or a vapor state.
The refrigerant that has flowed out of inflow paths is in a
gas-liquid two-phase state, in which the refrigerant has not
completely condensed. By making the refrigerant that has flowed out
of the inflow paths flow into connection pipes 151 and flow
downward or upward in the connection pipes 151, influences of
gravity on the refrigerant between the paths can be reduced and
formation of a liquid pool at lower paths can be inhibited.
As shown in FIGS. 5 and 6, the headers 130 are constituted by a
distribution/collection header 131 and a fold back header 132 that
bundle the heat-transfer pipes 112 at opposite ends thereof. The
distribution/collection header 131 distributes/collects refrigerant
to/from the heat-transfer pipes 112.
The distribution/collection header 131 includes a part called
distribution section 133 that distributes refrigerant flowing from
the outside into the distribution/collection header 131 to the
inflow paths 121 when the heat exchanger 101 is used as a
condenser. The distribution/collection header 131 further includes
a part called collection section 134 that collects the refrigerant
flowing out of the outflow paths 122 and discharges the refrigerant
to the outside when the heat exchanger 101 is used as a
condenser.
As shown in FIG. 6, the interior of the fold back header 132 is
divided by partition plates 135 into compartments each of which is
assigned to respective one of the inflow paths 121 and the outflow
paths 122. The fold back header 132 is provided with the connection
pipes 151. The interior of the distribution section 133 is divided
by the partition plates 135 into compartments each of which is
assigned to respective one of the inflow paths 121 in a similar
manner to the fold back header 132. The interior of the collection
section 134 is divided by the partition plates 135 into
compartments each of which is assigned to respective one of the
outflow paths 122 in a similar manner to the fold back header
132.
As shown in FIGS. 5 and 6, the connection pipes 151 are constituted
by down-flow pipes 152 and up-flow pipes 153. The down-flow pipes
152 and the up-flow pipes 153 have the same cross section. In FIGS.
2 and 3, illustration of the connection pipes 151 is omitted for
convenience of drawing.
Each down-flow pipe 152 allows, in the fold back header 132, the
compartment on the outlet side of a corresponding inflow path 121
(outlet-side compartment AR1 of the corresponding inflow path 121)
to communicate with the compartment on the inlet side of a
corresponding outflow path 122 (inlet-side compartment AR2 of the
corresponding outflow path 122) located below the corresponding
inflow path 121, via the down-flow pipe 152.
Each up-flow pipe 153 allows the outlet-side compartment AR1 of a
corresponding inflow path 121 to communicate with the inlet-side
compartment AR2 of a corresponding outflow path 122 located above
the corresponding inflow path 121, via the up-flow pipe 153.
In the present embodiment, the uppermost inflow path 121
communicates with the lowermost outflow path 122 via one of the
down-flow pipes 152. The lowermost inflow path 121 communicates
with the uppermost outflow path 122 via one of the up-flow pipes
153.
The second uppermost inflow path 121 communicates with the second
lowermost outflow path 122 via one of the down-flow pipes 152. The
second lowermost inflow path 121 communicates with the second
uppermost outflow path 122 via one of the up-flow pipes 153.
When the heat exchanger 101 is used as a condenser, the
high-temperature, high-pressure gas refrigerant introduced into the
distribution section 133 of the distribution/collection header 131
condenses into gas-liquid two-phase refrigerant, which is a mixture
of gas refrigerant and liquid refrigerant, by exchanging heat with
air while passing through the inflow paths 121. The gas-liquid
two-phase refrigerant is introduced from the outlet-side
compartments AR1 of the inflow paths 121 in the fold back header
132 into the inlet-side compartments AR2 of the outflow paths 122
in the fold back header 132, via the down-flow pipes 152 or the
up-flow pipes 153. The gas-liquid two-phase refrigerant in the
inlet-side compartments AR2 of the outflow paths 122 condenses
further into gas-liquid two-phase refrigerant in which liquid
refrigerant is dominant, by exchanging heat with air when passing
through the outflow paths 122.
The pressure of refrigerant flowing downward in the down-flow pipes
152 increases as the refrigerant moves from the outlet-side
compartments AR1 of the inflow paths 121 to the inlet-side
compartments AR2 of the outflow paths 122. This partially cancels a
decrease in the pressure of refrigerant flowing upward in the
up-flow pipes 153, resulting in a decrease in the pressure
difference .DELTA.p due to influences of gravity.
As a result, the pressure difference .DELTA.p in the vertical
direction in the heat exchange section 110 is decreased, inhibiting
formation of a liquid pool of refrigerant in lower heat-transfer
pipes 112. This allows for exchanging heat with
high-efficiency.
Next, a description will be given of the flow rate of refrigerant
circulating in the air conditioner 1.
Hereinafter, the amount of refrigerant circulating per second when
the air conditioner 1 is in operation at a rated cooling capacity
of the air conditioner 1 is referred to as refrigerant circulation
flow rate Gr [kg/s], and the number of inflow paths 121 to which
the distribution/collection header 131 distributes the refrigerant,
i.e., the number of branches of the distribution section 133, is
referred to as the number of paths N. The number of paths N is
equal to the number of outflow paths 122 and the number of
connection pipes 151. The rated cooling capacity of the air
conditioner 1 refers to an output of the air conditioner 1 when
room air is cooled to a temperature of 27.degree. C., under the
condition where a temperature of outdoor air is 35.degree. C. and a
relative humidity of the room air is 45%.
FIG. 7 is a graph illustrating the relationship between the
refrigerant circulation flow rate per path (flow channel) Gr/N
[kg/s] and the pressure loss .DELTA.P [kPa] in the connection pipes
151.
FIG. 7 shows that as the refrigerant circulation flow rate per path
Gr/N [kg/s] increases, the pressure loss .DELTA.P [kPa]
increases.
The pressure loss .DELTA.P [kPa] of the heat exchanger 101 is
derived from the pressure loss in the heat-transfer pipes 112 and
the pressure loss in the connection pipes 151.
It is required that the pressure loss in the connection pipes 151
be inhibited to such a degree that the power consumption of the air
conditioner 1 is not increased. This is because the connection
pipes 151 are not portions for exchanging heat between the
refrigerant and air positively.
From calculations, it is derived that the refrigerant circulation
flow rate per path Gr/N [kg/s] is preferably less than or equal to
0.035.
In other words, influences of pressure loss by the connection pipes
151 can be inhibited by setting the refrigerant circulation flow
rate Gr of the air conditioner and the number of paths N so as to
satisfy Inequality 1. N.gtoreq.Gr/0.035 Inequality 1
As described above, the connection pipes 151 are constituted by the
up-flow pipes 153 and down-flow pipes 152. The refrigerant flowing
through the connection pipes 151 is being condensed and thus is in
the form of gas-liquid two-phase refrigerant, which is a mixture of
gas refrigerant and liquid refrigerant. A certain flow rate is
necessary for the gas-liquid two-phase refrigerant including liquid
refrigerant mixed therein to flow upward in the up-flow pipes 153,
to move into the inlet-side compartments AR2 of the outflow paths
122 located on the upper side. Thus, the flow rate of the
refrigerant will be discussed next.
The Froude number Fr is known as an index for estimating a rising
limit of a liquid. The Froude number Fr is calculated by Equation
2: Fr=(.rho.GuG2+.rho.LuG2)/(.rho.Lgd) Equation 2 where .rho.L is
the density of the liquid refrigerant, .rho.G is the density of the
gas refrigerant, uG is the flow rate of the gas refrigerant, g is
the gravitational acceleration, and d is the inner diameter of the
pipe.
By setting the flow rate of gas-liquid two-phase refrigerant such
that the Froude number Fr takes a value greater than or equal to a
predetermined value (=1), the gas-liquid two-phase refrigerant
including liquid refrigerant mixed therein is able to flow upward
in the up-flow pipes 153.
When the Froude number Fr is less than the predetermined value
(=1), the mixed liquid refrigerant adheres to the wall surfaces of
the up-flow pipes 153 and is unable to flow upward further. As a
result, liquid pools are formed in the outlet-side compartments AR1
of the inflow paths 121 located on the lower side.
To obtain a Froude number Fr of a predetermined value (=1) or
greater, it is necessary that the refrigerant circulation flow rate
per path Gr/N [Kg/s] be greater than or equal to 0.003 [kg/s] (see
FIG. 8).
Therefore, in combination with the conditions described above, it
is required to determine the number of paths N with respect to the
refrigerant circulation flow rate Gr such that the refrigerant
circulation flow rate per path Gr/N [Kg/s] satisfies Inequality
3.
This inhibits the pressure loss .DELTA.P [kPa] due to the
arrangement of connection pipes 151 and inhibits formation of
liquid pools in the connection pipes 151.
0.003.ltoreq.Gr/N.ltoreq.0.035 [kg/s] Inequality 3
Next, a description will be given of the configuration of the
connection pipes 151.
The connection pipes 151 are not limited as to their cross
sectional shape, but are configured as having their hydraulic
diameter D in the range given by Inequality 4. 4.ltoreq.D.ltoreq.11
[mm] Inequality 4
The range of hydraulic diameter D represented by Inequality 4 is
derived from FIGS. 9 and 10.
FIG. 9 shows the relationship between the hydraulic diameter D [mm]
of the connection pipes 151 and the pressure loss .DELTA.P [kPa] in
the connection pipes 151, in three conditions that satisfy
Inequality 3.
From FIG. 9, it is obvious that, in a region where the hydraulic
diameter D is less than a certain value, as the refrigerant
circulation flow rate Gr increases, the pressure loss .DELTA.P
[kPa] increases. From FIG. 9, to reduce the influence of the
pressure loss .DELTA.P [kPa] for any refrigerant circulation flow
rate Gr and the number of paths N, it is preferable that the
hydraulic diameter D of the connection pipes 151 be 4 mm or
greater.
Incidentally, when the connection pipes 151 have a larger hydraulic
diameter D, radius for bending the connection pipes 151 needs to be
increased. As a result, a larger space is required for installing
the heat exchanger 101. However, the space for installing the heat
exchanger 101 is limited. Thus, it is desirable that the heat
exchanger 101 be as small as possible.
In addition, from FIG. 10, it is obvious that as the hydraulic
diameter D of the connection pipes 151 increases, the amount of
refrigerant held per connection pipe increases. An increase in the
amount of refrigerant held increases production cost of the air
conditioner 1 as a whole. For this reason, it is desirable not to
hold more than necessary refrigerant.
For this reason, taking into account the installation of heat
exchanger 101 in a machine casing (not shown) or the like of the
outdoor unit 10, it is preferable to select pipes having a
hydraulic diameter D of 11 mm or less as the connection pipes
151.
In view of the foregoing, the connection pipes 151 are configured
such that the hydraulic diameter D thereof falls within the range
given by Inequality 4.
Next, a description will be given of the effects of the heat
exchanger 101 according to the present embodiment.
In the heat exchanger 101 according to the present embodiment, the
inflow paths 121 and the outflow paths 122 are connected via the
connection pipes 151 such that at least one of the inflow paths 121
communicates with one of the outflow paths 122 located below the at
least one of the inflow paths 121, and at least another one of the
inflow paths 121 communicates with another one of the outflow paths
122 located above the at least another one of the inflow paths
121.
With this configuration, an increase in the pressure of refrigerant
flowing downward in the down-flow pipes 152 cancels at least some
of the decrease in the pressure of refrigerant flowing upward in
the up-flow pipes 153, resulting in a decrease in the pressure
difference .DELTA.p due to influences of gravity.
As a result, the pressure difference .DELTA.p in the vertical
direction in the heat exchange section 110 is decreased, inhibiting
formation of liquid pools of refrigerant in the heat-transfer pipes
112 located on the lower side. This allows for exchanging heat with
high-efficiency.
In the heat exchanger 101 according to the present embodiment, the
refrigerant circulation flow rate per path Gr/N [Kg/s] is adjusted
so as to fall within the range given by Inequality 3.
This inhibits formation of liquid pools in the heat-transfer pipes
112 and allows for exchanging heat (condensation of thermal medium)
with high-efficiency.
In the heat exchanger 101 according to the present embodiment, the
connection pipes 151 are configured to have a hydraulic diameter D
falling within the range given by Inequality 4.
Selecting a hydraulic diameter D of 4 mm or greater reduces
influence of the pressure loss of the refrigerant flowing through
the connection pipes 151.
Selecting a hydraulic diameter D of 11 mm or smaller contributes to
space saving of the device as a whole. Further, configuring the
connection pipes 151 to have a hydraulic diameter D of 11 mm or
smaller inhibits the amount of thermal medium held in the
connection pipes 151, leading to cost reduction of the device as a
whole.
In the heat exchanger 101 according to the present embodiment, each
heat-transfer pipe 112 is constituted by a flat tubular member with
a cross section having a substantially oval shape.
With this structure, each heat-transfer pipe 112 can have a smaller
cross-sectional area than a circular cylindrical pipe having the
same surface area, and thus can reduce the amount of the thermal
medium to be held, even with the same surface area (heat exchange
area) as that of the circular cylindrical pipe.
In addition, the interior of each heat-transfer pipe 112 is divided
into the plurality of flow channels 114 by the partition walls 113
to increase the area where the thermal medium and the heat-transfer
pipe 112 are in contact with each other.
This increases the amount of heat to be exchanged without
increasing the amount of the thermal medium to be held.
In the heat exchanger 101 according to the present embodiment, it
is preferable to use at least one of the refrigerants: R410A,
R404A, R32, R1234yf, R1234ze(E), and HFO1123 as the thermal
medium.
These refrigerants have an ozone depletion potential of zero.
Selecting at least one of those refrigerants on the basis of the
necessary refrigeration capacity and operation temperature allows
for ensuring refrigeration capacity at any evaporation pressure. As
a result, the embodiment allows for reducing the amount of the
refrigerant to be held compared to that in conventional heat
exchangers.
It should be noted that, in the present embodiment, although the
configuration of the invention of the present application is
applied to a fin-tube type heat exchanger, the invention of the
present application is not limited thereto. The invention of the
present application is applicable to any heat exchanger in which a
plurality of heat-transfer pipes extending in the horizontal
direction and spaced apart at predetermined intervals in the
vertical direction are arranged and the plurality of heat-transfer
pipes are used (assigned) as a plurality of paths via headers.
Examples of such a heat exchanger include corrugated fin type heat
exchangers. The invention of the present application applied to
such a heat exchanger is able to achieve the same effects.
Although, in the present embodiment, the connection pipes 151 are
arranged such as to be exposed outside the fold back header 132,
the present application is not limited thereto.
For example, as shown in FIG. 11, connection pipes 151A can be
arranged inside the fold back header 132.
With this configuration, as the fold back header 132 has no
irregularity on the external side, the heat exchangers 101 are
easily arranged in casings of the outdoor unit 10 and the indoor
unit 30.
In the present embodiment, the number of heat-transfer pipes 112
constituting each inflow path 121 is the same as the number of
heat-transfer pipes 112 constituting each outflow path 122.
However, the present invention is not limited thereto. It is
possible to assign different number of heat-transfer pipes 112 to
them.
For example, as described above, in a condenser, the ratio of gas
refrigerant to the whole refrigerant is high upstream of the heat
exchange section 110, whereas the ratio of liquid refrigerant to
the whole refrigerant increases as the refrigerant flows
downstream. Thus, the volume of the refrigerant in each outflow
path 122 is smaller than that in the corresponding inflow path
121.
Taking this into account, each inflow path 121 may be constituted
by a larger number of heat-transfer pipes 112 than those
constituting each outflow path 122.
With this configuration, when the heat exchanger 101 is used as a
condenser, the area where gas refrigerant gives off heat is large,
improving the heat-exchange efficiency.
That is, in the inflow paths and the outflow paths, it is desirable
to select the number of heat-transfer pipes used in each outflow
path and the number of folding back and the like, in accordance
with the distribution of warm air speed and expected heat exchange
state of refrigerant. Those numbers may not be necessarily the same
between the inflow paths and the outflow paths.
Next, a description will be given of another embodiment of a method
of evaluating the flow rate of the refrigerant circulating in the
heat exchanger 101.
The heat exchanger 101 has the same configuration as that of the
above-described embodiment. That is, the connection pipes 151 are
configured to have a hydraulic diameter D [mm] falling within the
range given by Inequality 4.
The present embodiment differs from the above-described embodiment
in that the former defines a condition for gas-liquid two-phase
refrigerant including mixed liquid refrigerant to flow upward in
the connection pipes 151 in terms of a rated cooling capacity Q
rather than a refrigerant circulation flow rate Gr in relation with
the Froude number Fr.
The rated cooling capacity Q refers to an output of the air
conditioner 1 when room air is cooled to a temperature of
27.degree. C., under the condition where a temperature of outdoor
air is 35.degree. C. and a relative humidity of the room air is
45%.
As physical properties used for calculating the Froude number Fr
vary per refrigerant to be used, the obtainable enthalpy difference
and density change. For this reason, depending on the type of the
refrigerant, gas-liquid two-phase refrigerant may possibly not flow
upward in the connection pipe 151 even when the refrigerant
circulation flow rate Gr derived from Froude number Fr falls within
the range given by Inequality 3.
In view of this, the present evaluation method uses the rated
cooling capacity Q [kW] as an index that substitutes for the
refrigerant circulation flow rate Gr [kg/s].
Inequality 5 expresses a range corresponding to the range given by
Inequality 3. 0.75.ltoreq.Q/N.ltoreq.3.5 [kW] Inequality 5
Controlling the rated cooling capacity per path Q/N to fall within
the range given by Inequality 5 achieves the same effects as those
intended by Inequality 3, even with refrigerant having different
physical properties.
That is, gas-liquid two-phase refrigerant is able to flow upward in
the connection pipes 151 and formation of liquid pools in the
connection pipes 151 can be inhibited.
Therefore, formation of liquid pools in the heat exchanger 101 can
be inhibited and an appropriate amount of refrigerant can be sealed
while improving the heat-exchange efficiency.
Reference Signs List
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